16. POWER CIRUCIT
16-1. Circuit Configuration
(1) Block diagram
V~
Rectifier
~
__
J~
Seri~1
11-------00
-
-I
. 1 regu
ator
-12V
(2)
The above figure, an
AC
input
of
SO/60Hz
is
rectifi-
ed into a
DC
current which
is
then
converted into an
alternate current
of
50
kHz
to
produce
+5
V and
+ 12 V
output
voltages. For
the
control
of
the
output
voltage, the
output
voltage
is
detected and controlled
of its pulse width
to
drive
the
transistor in
the
power
switching section.
As
for
-12
V,
and AC input
of
50/60
Hz
is
rectified into a
DC
current
of
which
voltage
output
is
stabilized by
the
serial regulator.
16-2. Description
of
the Power Supply Circuits
(1) Rectifier circuit
____
-12V
circuit
RC2
(RCt)
,.---------,
I I
I
DC29V
(29V)
4}-
AC22.5V
(21.5V)
u--~:~~~~-'-~I-~-~LO
L
_________
.J
Fig. 1 Rectifier
circuit
Figure 1 shows
the
rectifier circuit. Input of
AC
local
voltage
for
the
power transformer
is
converted into
the
secondary
output
voltage
of
22.5 V
AC
and rectified
to
obtain
29V
DC
from which deriverd
+5V
and
+12V
outputs. Enclosure by dotted line
in
Fig. 1 shows the
-12
V rectifier circuit.
(2)
+5V
power switching
04
C9
Fig. 2 Power switching
In
Fig.
2,
S1
is
connected
to
the
base
of
04
and the
current ION flows through when
03
becomes active.
When
03
turns inactive,
the
current IOFF flows
through. So, by controlling
the
on/off
time ratio, it
-80-
produces a stable voltage supply.
Fig. 3 shows
the
03
driving circuit.
1) When
05
turns active,
the
current ION flows
through
in
the
direction shown with the solid
line
and makes Q3 and Q4 active.
2) When
05
turns
inactive,
the
current IOFF flows
through
in
the
direction shown with
the
broken
line
and makes Q3 and
04
reverse biased so
as
to
delay
speed
of
Q3
at
the
falling edge.
Q4
base
+12V
S2
L,......;~
___
-oOV
Fig. 3 Driving
circuit
(3)
+12V
power switching
This driving circuit performs
the
same
as
the +5V
power switching action by means of
06.
07
is
driven by
M1
(8 and
11
pins). (Fig. 4)
(4)
-12V
output
control
In
this circuit
the
unstable voltage supply from the
power transformer
is
obtained the stable supply of
-12V
via
the
dropper.
If
the
output
is
lower than the
reference voltage, it makes the 01 base current increas-
ed
so
as
to
rise
the
output
voltage.
If
it
is
higher, the
base current
is
supplied
to
D1
to
increase the 01
resistance so
as
to
restrict
the
output
voltage.
In
this
manner,
the
output
voltage supply
is
maintained
to
a
stable level. (Fig. 5)
I
PSP293~
M1
#8
and
11
pins
o-----~-------oOV
Fig.4
Drive
circuit
_-
.......
--ooV
01
R2
C2
Q------~---~--o-12V
Fig. 5
-12V
output
control
circuit
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